Environmental investigation report of Hongze Lake

With the strengthening of the research on the impact of global environmental change, especially the deepening of the research on human activities and the relationship between man and land, the research on ecological vulnerability, ecological vulnerable areas and vulnerability assessment has become more and more extensive. As a new research field, its mechanism and influencing factors are still under discussion. In 1905, Elements introduced the term ecotone in ecology, and ecologists used it to refer to the ecotone between different communities. It is a sudden transition area between two relatively uniform adjacent communities, an area where edge effect and biodiversity occur, and an important restricted area for biological distribution and animal activities. In 1987, the ecotone is recognized as a new concept "ecotone" [1 ~ 3]. Since 1980s, with the development of ecology, especially the rise of landscape ecology, ecological ecotone has received new attention from ecologists. From the late 1980s to the mid-1990s, scholars in the fields of geosciences and environment in China introduced the idea of transition zone into their respective studies, and formed the concepts of eco-environmental fragile zone or eco-environmental fragile zone or eco-environmental transition zone, so ecological vulnerability evolved from community transition zone.

1 explanation of ecological vulnerability

The connotation of 1 1 ecological vulnerability

At present, there are many explanations for the ecological fragile environment in China, but this paper holds that the ecological fragile environment should belong to the broad category of natural and humanistic understanding and is an inherent natural attribute of the ecological environment. The normal function of the ecosystem is disrupted and exceeds the "threshold" of elastic self-regulation, which leads to the destruction of the feedback mechanism and the irreversible change of the system, thus losing its resilience; When it exceeds the current socio-economic and technological level and can maintain the current level of human utilization and development for a long time, it is called ecologically fragile environment. That is to say, under the condition of maintaining and improving the degree and scale of human utilization of the environment, environmental degradation and resource depletion can be alleviated through economic and technological reform and adjustment, or through importing or exporting resources, thus linking regional and global issues. This broad understanding of ecologically fragile environment is of universal significance. Therefore, when the degradation of ecological environment exceeds the existing socio-economic and technological level, and the current level of utilization and development of human beings cannot be maintained for a long time, it is called "ecologically fragile environmental area".

Ecological fragility is the response of a specific ecosystem to external interference in time and space scale, and it is the result of natural factors or human short-term economic behavior. In a strict sense, the concept of ecological fragility focuses on highlighting the degree to which the ecosystem deviates from the original environment, that is, the unstable characteristics of the ecological environment after external interference. Eco-environmental vulnerability includes structural vulnerability and pressure vulnerability. Structural fragility is mainly determined by the structure of the system itself, which is mainly reflected in the instability and sensitivity of the system itself; Pressure fragility refers to the driving force that leads to system fragility, mainly the adverse impact of external environmental disturbance on the system. According to various dynamic sources that induce system vulnerability, pressure vulnerability can be divided into two types: human activity pressure and environmental pressure [3 ~ 5]. Therefore, not all ecotones are ecologically fragile environments, but only a kind of sensitive environment, and only sensitive environments with degradation trends are called ecologically fragile environments. The so-called ecological fragility refers to the environmental degradation, landscape deterioration, land productivity decline, land resource loss, etc. caused by the joint action of nature and human activities including society, economy and technology in an ecologically fragile area or zone, which is characterized by the fact that the current level of human utilization and development cannot be maintained for a long time.

1.2 Mechanism and characteristics of ecological vulnerability

The fragility of the ecological environment comes from the sensitivity of the environment, which refers to the sensitivity of the environment to external interference. Vulnerability is an inherent feature of some ecosystems, but it is also directly or indirectly related to external interference. Vulnerability refers to the adaptability and ability of an ecosystem, landscape or regional environment to external interference. Specifically, it refers to the probability that environmental problems will occur under the same intensity of non-benign human activities or external forces, focusing on the degree to which the ecosystem deviates from the original environment. The greater the vulnerability, the more sensitive it is to non-benign interference, which has amplification effect; It is passive to benign interference (recovery and reconstruction) and the conversion efficiency is low. The environmental status of fragile habitats depends on the degree of land use, which can be divided into excellent, medium and poor, but its resilience is fragile, and its fragility, sensitivity and irrecoverability determine that the most fragile habitat is degraded habitat. Eco-fragile environment is closely related to nature, society and economy, and it is the result of the interaction and influence of natural environmental conditions, production activities and historical development process. It reflects the natural population carrying capacity of different landscape types, geographical systems and regions, and reflects the sensitivity of natural environment to human interference and the weakness of human economy [5, 6]. For economically developed areas, human vulnerability plays a leading role, and the ecological environment also shows vulnerability.

The fragile zone of ecological environment has the following basic characteristics: ① the probability of being replaced is high, the degree of competition is high, and the chance of restoring to the original state is small; (2) the anti-interference ability is weak, and the external force that changes the interface state has relatively low impedance; (3) The interface changes quickly and has strong spatial fluidity; ④ It is a nonlinear concentrated expression area and a discontinuous concentrated display area, which is the area where mutation occurs; ⑤ It is the occurrence area of biodiversity. In the natural ecological environment, geology, landform, climate, hydrology and soil combination show different particularities, so the macro fragile ecological environment has the following spatial manifestations: urban-rural transition zone, dry-wet alternate zone, farming-pastoral ecotone, land-water boundary zone, forest edge zone, desert edge zone, gradient connection zone and landform plate contact zone [6,7]. Wetland, known as the "kidney of nature", is a unique water resource and ecosystem formed under the interaction between land and water, and is a typical land-water junction area. In recent decades, due to the frequent interference of human activities, wetlands have shown their own ecological vulnerability characteristics. Therefore, we have reason to believe that studying the ecological fragility of wetlands is conducive to the rational development and protection of wetland resources and has important practical significance for realizing the sustainable development of wetlands.

2 Overview of Hongze Lake Wetland

2. Geographical features of1

Hongze Lake Wetland is the largest lake wetland in Huaihe River Basin, and it is also one of the five largest freshwater lakes in China and the fourth largest freshwater lake. Located in the northwest of Jiangsu Province, the geographical location is 33 06 ′ ~ 33 40 ′ north latitude and118/kloc-0 ′ ~165438 east longitude. Wetlands are under the jurisdiction of Hongze, Huaiyin, Xuyi, Siyang and Sihong counties. Looking at the low mountains and hills in the south, the abandoned Yellow River in the north, the Grand Canal in the east and the undulating plains in the west. Hongze Lake Wetland, which flows into Huaihe River in the west, Yangtze River in the south, Yellow Sea in the east and Yishu River system in the north, receives water from the middle and upper reaches of Huaihe River 1.58 million km[2], and is the connection point of the middle reaches, tributaries and downstream rivers of Huaihe River. Physically, it belongs to the transition zone of the middle and lower reaches of the Yangtze River in the north subtropical zone of the warm temperate Huanghuaihai Plain. As a large shallow lake reservoir in plain area, Hongze Lake Wetland has a water area of 1597km[2] and a volume of 135m[3][8 ~ 10]. Located in the transitional zone between the north subtropical zone and the south warm temperate zone in China, it is a typical wetland in Jianghuai area and even the middle and lower reaches of the Yangtze River with distinct seasons, remarkable monsoon, abundant animal and plant resources, unique geographical location and diverse functions.

2.2 Characteristics of biodiversity

The species diversity of Hongze Lake wetland includes plant diversity and animal diversity. Wetland nature reserve has a vast ecosystem, alternating land and water, mild climate and rich biological species. There are 8 phyla 14 1 genus 165 species of phytoplankton. Among the phytoplankton in wetland, algae belong to 7 phyla, 36 families and 98 genera, among which Chlorophyta is the most, followed by cyanobacteria and diatoms, Chlorella and Cryptophyta are the least. Phytoplankton is almost all over the lake. There are many kinds of aquatic plants in wetlands, covering a wide area. There are 36 families, 665,438+0 genera and 865,438+0 species of aquatic higher plants, among which reed, calamus and other genera are the most, and different families and genera have their own growth and distribution laws.

Hongze Lake wetland is rich in bird and animal resources, including zooplankton in 35 families, 63 genera and 9 1 species, zoobenthos in 3 classes, 6 families and 7 species, molluscs in 25 genera and 43 species, arthropods in 3 classes, 22 families, 25 genera and 25 species, and the migratory bird population exceeds 50,000, including 5 species under national first-class protection and national second-class protection. There are many kinds and quantities of creatures, which are well preserved. Red-crowned cranes, white cranes, cygnets and white-naped cranes all come here for the winter after mid-June+10 every year. In addition, there are wild ducks, geese, monitor lizards, badgers and hedgehogs in the wetland. There are many rare and endangered species in Hongze Lake Wetland (Table 1). According to the investigation records of Hongze Lake wetland in 1992, there are 84 species of fish in 16 families in the wetland, which is an important freshwater fish area in China and is known as the "live fish bank". Carp, mandarin fish, crucian carp and whitebait are the most economical fish, among which whitebait has high nutritional value. There are many grass shrimps in the wetland, including green shrimp, white shrimp, serrated rice shrimp, grass shrimp and Lagu shrimp, among which green shrimp is the most, accounting for 38% of the total shrimp. Eriocheir sinensis is the most common crab. In addition, there are 69 genera, 32 families and 4 phyla of zooplankton, and 76 species of zoobenthos [8 ~ 13]. Therefore, protecting Hongze Lake wetland will play a positive role in protecting Hongze Lake, an important strategic water resource in northern Jiangsu, and improve the water quality of the East Route of South-to-North Water Transfer Project. The China Biodiversity Conservation Action Plan formulated by China in 1994 listed "Hongze Lake Wetland in Jiangsu" in the priority list of "Building a new nature reserve in areas where biodiversity is in urgent need of protection", and the Development Plan of China Nature Reserve also listed Hongze Lake Wetland in the construction plan of national nature reserves. However, because Hongze Lake belongs to the middle and lower reaches of Huaihe River basin, droughts and floods are frequent, and the ecological vulnerability of wetlands mainly includes natural vulnerability and human disturbance vulnerability. The specific characteristics and reasons are as follows.

Table 1 Protection Grade of Chinese Names of National Key Protected Wild Animals in Hongze Lake Wetland

White crane level 1 cygnet level 2

Red-crowned crane, swan, swan.

Great bustard, level one, mandarin duck, level two.

Heihe primary crane secondary crane

First-class white-headed bustard and second-class white-naped crane

3 Hongze Lake wetland ecological vulnerability characteristics

The ecological vulnerability of Hongze Lake wetland can be divided into basic vulnerability, interface vulnerability and fluctuation vulnerability according to the causes. Basement vulnerability mainly emphasizes the special geological and ecological environment of wetland, interface vulnerability emphasizes the gradient change of elements in the spatial direction of wetland, and fluctuation vulnerability emphasizes the drastic change of elements in time series.

3. 1 Geomorphic basement fragility

The fragility of basement emphasizes the special geographical background of the formation of Hongze Lake. Hongze Lake is a relatively young lake, originally formed in12nd century. In history, due to the interference of the Yellow River from Huaihe River to the sea many times, Hongze Lake became a famous "aboveground lake" after its formation. Hongze Lake became an "overground lake" because the ancient Yellow River invaded the Huaihe River into the sea. More than 800 years ago, the Huaihe River was a big river that entered the sea alone. In the second year of Jianyan in the Southern Song Dynasty (A.D. 1 128), the Yellow River seized the Huaihe River waterway, bringing a lot of sediment to the Huaihe River and gradually blocking it. In 1 194, the Yellow River once again seized the lower reaches of the Huaihe River and entered the sea, making it even more difficult for the Huaihe River to vent. The water flowing down from the middle and upper reaches of Huaihe River finally stayed in the east of Xuyi, and soon became a wide Hongze Lake. The Yellow River did not change its course northward until 1850, during which the sediment concentration in Huaihe River became higher and higher. After the formation of Hongze Lake, the velocity in the middle and upper reaches of Huaihe River decreased sharply and the sediment transport capacity weakened. A large amount of sediment sank to the bottom of the lake, making the bottom of the lake rise day by day. People by the lake have to constantly raise and reinforce dams to prevent floods. At present, the levee of Hongze Lake has been raised to the height of 16m, and the height of the lake bottom is also above 10.5m, which exceeds the average elevation of He Lixia Plain in the east of the lake less than 9m and becomes a "suspended lake" [1 1 2].

At present, the Hongze Lake basin is shallow dish-shaped, with a flat lake bottom and an altitude of about 10.5 meters ... On the other hand, the western part of Hongze Lake is a wavy terrain with alternating ridges and depressions, and a series of four ridges and three shallow depressions extending in the northwest-southeast direction are arranged in parallel. Moreover, its general trend is low in the west and high in the east, high in the north and low in the south, and the lake basin inclines from northwest to southeast, which is consistent with the general trend of Huanghuai Plain where Hongze Lake is located. In addition, because Hongze Lake is located in the middle and lower reaches of Huaihe River, its upstream main stream is 850km long, but the slope is only 0.03% ~ 0.5%. This landform basement with high west and low east and the characteristics of "hanging lake" make Hongze Lake itself a fragile body, which is not conducive to flood discharge. Once the upstream inflow is too large or there is heavy precipitation, it will make the lake area vulnerable to floods, so Hongze Lake will become an area affected by floods.

3.2 the fragility of the transition zone interface

Interface is generally understood as a sudden transition between relatively balanced elements or the adjacency of abnormal spaces, and is sometimes called "transition zone" or "edge zone". As a water body, Hongze Lake is a water-land-air interface, and its influencing factors are very extensive. Geographically speaking, Hongze Lake is located in the junction of the northernmost subtropical zone and the southernmost warm temperate zone in China, and it is a transitional zone between subtropical and warm temperate climate zones. At the same time, Hongze Lake is located on the Qinling-Huaihe line, which is an important dividing line of the physical geography of the north-south transition zone in China and belongs to a typical marginal transition zone. In this area, many elements of its physical geography, including climate, hydrology, vegetation and even human factors, have universal particularity.

The average sunshine rate in Hongze Lake area is 52%. Annual average temperature 14.8℃, minimum temperature-16. 1℃, maximum temperature 39.8℃. The annual average water temperature is 15.6℃. The source of water vapor in the lake area mainly comes from the southwest Indian Ocean and the Bay of Bengal in the western Pacific Ocean. With the input of southwest monsoon and southeast monsoon, some water vapor is also imported from the Yellow Sea and the East China Sea. The main weather systems of precipitation in the lake area include shear line, vortex, typhoon, cold wind in low trough and vortex in north trough. The monsoon in Hongze Lake basin is remarkable, and the southeast monsoon jumps to the north and retreats to the south, with great differences in dry, wet, cold and warm years. In summer and autumn, it is affected by the warm and humid air flow in the Pacific Ocean and the cold air in the north, and there are often concentrated heavy rains and persistent heavy rains, and it is also often affected by typhoons. In winter, cold air from the north invades the south, the climate is dry and cold, and precipitation is scarce. In terms of precipitation, Hongze Lake area is in the transition zone between the south with abundant rainfall and the north with little rainfall. The temporal and spatial distribution of precipitation is uneven, and the interannual variation is drastic. The maximum annual precipitation is 1240.9mm( 1965). The minimum annual precipitation is 532.9mm( 1978). There are generally three rainy seasons every year, namely spring rain (May), plum rain (June-July) and autumn rain (September). It is particularly noteworthy that the meiyu stagnation in June-July in some years in Jianghuai led to long-term and large-scale precipitation, which led to floods. However, in some years, the subtropical high is too strong or the Siberian cold air mass is too strong, which leads to dry climate. These meteorological factors in Hongze Lake reflect the characteristics of interface fragility in the transitional zone [8, 12, 13].

3.3 Vulnerability of alternating fluctuation of drought and flood disasters

Volatility vulnerability is characterized by the repeated combination of different states in the number of objective entities, but there is no substantial change in nature. Fluctuation is both a manifestation and a cause of vulnerability. Historically, floods and droughts occurred frequently in Hongze Lake area [12 ~ 15], which is also the main reason for the obvious vulnerability of Hongze Lake area.

According to Yang Qingping's research on the water level change of Hongze Lake in recent 50 years, the years when the water level of Hongze Lake is ≤ 1 1.3m are 1957, 1959, 19 1 respectively. 1992, 1994, 1995, 1997, 1999, 200 1 * * 20 years, in which, The years when the water level of Hongze Lake is ≤ 1 1.0m are 1955, 1959 and 65438. According to the analysis of hydrological data since Hongze Lake 1736, the occurrence of floods since 1736 can be roughly divided into the following categories. The annual maximum water level is greater than 15.0 feet (a ruler was built in Qing dynasty, which is equivalent to 0.32m per foot, The following flood years are 1742, 1753, 1755, 177 1, 1773, 1778 and/kloc-respectively. ②1805 ~1851year. The flood years with annual maximum water level greater than 20.0 feet are 183 1 ~ 1833, 1839, 1840, 184 1,/kloc-. Among them, 185 1 year (one year in Qing Xianfeng) is the highest, and the length of high weir water pile is 23.4 feet. The masonry and levee in Hongze Lake are very dangerous. ③1852 ~1911year. 1906 (thirty-two years of Guangxu in Qing dynasty) has the highest flood level, with heavy rain in summer and autumn. The inflow from the upper reaches of Hongze Lake is very strong, and the weir water reaches 16.6438+0 feet. ④ From 19 12 to now. In the past 100 years, there were 19 16 years, 192 1 year, 193 1 year, 1950 years. Combined with the historical drought and flood disasters in Hongze Lake, the flood disaster of 100 has obvious historical inheritance and continuity characteristics in time. This situation of alternating drought and flood disasters makes Hongze Lake wetland show obvious fluctuation characteristics. There are many reasons for the drought and flood disasters in Hongze Lake, so I won't go into details here.

3.4 Water pollution intervention is fragile

Hongze Lake is located in the middle and lower reaches of Huaihe River. To understand the water pollution situation of Hongze Lake, we must consider the surrounding areas of Hongze Lake, especially the upstream water bodies. Huaihe River enters Jiangsu boundary from Daliu Lane in Anhui Province and flows into Hongze Lake through Xuyi and Hongze Zi Long. Li Bo and others found that the inflow of Huaihe River into the lake accounts for more than 70% of the total inflow of rivers around Hongze Lake, and the pollutants entering the lake account for 80.4% of the whole lake. The water quality of Hongze Lake is basically polluted by the runoff of Huaihe River, including the counties along the lake and the water system of Hongze Lake. The mountainous areas including other provinces and cities are imported through Huaihe River, He Sui, He Sui and tributaries, and finally enter Hongze Lake from the water inlets of Huaihe River and Lihewa. However, pollutants mainly come from Huaihe River estuary and Lihewa, accounting for 80.4% and 14.39% respectively, while other rivers entering the lake only account for 1.57%. Among the local pollution sources entering the lake, Sihong, Xuyi and Siyang counties in the west of the lake are the main ones, and the wastewater discharge accounts for 56.38%, 32.49% and 1 1% respectively. Hongze and Huaiyin areas in the east of the lake are mostly rivers leaving the lake, with less pollutants entering the lake, and the share is generally less than 0. 1% [13, 15, 16].

The water pollution in Huaihe River basin is getting more and more serious. "Washing rice and vegetables in 1950s, washing clothes and irrigating in 1960s, deteriorating water quality in 1970s and rampant fish and shrimp in 1980s" is a true portrayal of water pollution in the main stream of Huaihe River. After the 1980s, many local departments and enterprises failed to seriously implement environmental protection policies, blindly developed small paper mills, small fertilizer plants and small tanneries with serious pollution, and a large amount of sewage and wastewater were directly discharged into rivers and lakes, resulting in widespread pollution of water bodies in river basins. The typical case is1July, 1994, which lasted for 55 days, with high concentration of pollutants, great toxicity, serious damage to the ecological environment and huge economic losses. About 70,000 Jin of fish and 3,000 Jin of crab died in Xuyi County in two days, and the county's fishery directly lost 63.5 million yuan, and the accumulated direct economic loss exceeded 65.438+0.7 billion yuan. During the period of 1996, 79.7% of the water quality in Huaihe River Basin was worse than Grade IV, of which Grade V+Super Grade V accounted for 64. 1%. Major pollution accidents occurred in the basin 160 [15, 17].

According to incomplete statistics, since 1970s, the water pollution accidents in Hongze Lake mainly include: ① Huaihe River estuary. 65438+May 0975,65438+May 0982,65438+March-April 0986,65438+February 0989,65438+1October 0989,65438+February 0992,65438. ② The entrance of Lihe depression into the lake. 65438+July 0974,65438+1October 0980,19865438+1October 00,65438+May 0986,65438+April 0987,/kloc-0. It can be seen that Hongze Lake, as a passing lake, its water quality change is mainly controlled by the incoming water from the upper reaches of Huaihe River, and the water quality change process of Hongze Lake is also a concentrated expression of the water pollution situation in Huaihe River Basin. This kind of external water pollution makes the ecological environment of Hongze Lake extremely fragile, and the water quality is polluted, which directly destroys the stability of aquatic ecosystem and land-water boundary ecosystem in the lake area.

3.5 The comprehensive impact of human activities is disturbing and fragile.

With the development of social and economic activities, various influences of human activities have rapidly penetrated into all parts of the Hongze Lake wetland basin ecosystem. The impact of human activities mainly includes the development of beaches, reclamation around lakes, cage culture in lakes, the use of chemical fertilizers and pesticides, and of course the above-mentioned water pollution incidents.

The evolution history of Hongze Lake dike itself is largely the result of human influence. In order to resist the flood disaster, human beings have built the Hongze Lake levee, and it has been continuously heightened. If there is a big flood disaster, its harm will be even greater. Hongze Lake belongs to gentle slope terrain, with alternating hills and depressions, which is easy to develop. Since the 1950s, due to the development of reclamation beaches, especially in recent years, fish, shellfish, crabs and shrimps have been cultured in cages in lakes, the water forms of Lihewa, Anhewa and Chengziwa in Hongze Lake have changed obviously, and the scope is shrinking day by day. At present, Lihewa and Chengziwa basically maintain their general lake bay shape, but the water area of Chengziwa is only 350km[2], and Anhewa basically disappears. The area of the lake area is reduced, especially the intake channel is narrowed, and the upstream incoming water leaks into the lake, which is more prone to floods, affecting the aquatic ecosystem, especially the safety of people's lives and property in the lake area [2 1, 22].

1984 The high density of purse seine culture in Houhu Lake increased the contents of nutrients such as nitrogen and phosphorus in water, accelerated the eutrophication process of the lake and promoted the growth and reproduction of some algae. Reclamation around the lake has changed the growth conditions of benthos, zooplankton and vegetation, resulting in the decrease of species and the imbalance of wetland ecological environment; Random fishing leads to the depletion of fishery resources and the destruction of aquatic animal habitats; Farmland irrigation makes full use of lake water resources, but it also reduces the environmental capacity of the lake area, and there is a contradiction between aquaculture and farmland irrigation [23, 24]. Therefore, in human development activities, it is necessary to restore and develop the biological resources of Hongze Lake, establish a virtuous cycle of wetland ecosystem, adhere to equal emphasis on development and protection, and make the economic development of the lake area sustainable.

4 Summary and discussion

As a typical ecological tune, Hongze Lake wetland has the characteristics of sensitivity, fragility, weak feedback regulation mechanism and poor stability [25]. The main reasons for the fragility, sensitivity and instability of the ecological environment in the Hongze Lake Basin are the uniqueness of its basement landform, the particularity of its geographical position at the important dividing line of China's physical geography, the frequent occurrence of droughts and floods, and the increasing influence of human activities, especially the characteristics of large fluctuation, poor stability and strong temporal and spatial variability of the water quality in the Huaihe River Basin and Hongze Lake. Therefore, it can be considered that the ecological environment vulnerability of Hongze Lake wetland is manifested in two forms: structural vulnerability and external interference stress vulnerability.

Hongze Lake wetland ecosystem is one of the important wetland ecosystems that need to be protected in China because of its complex types, diverse plant communities and various animal and plant resources, which play an important role in regulating regional water resources and water and heat balance. According to the vulnerability characteristics of Hongze Lake wetland, the wetland protection countermeasures mainly include controlling the upstream water quality and minimizing the pollution into the lake; Strengthen ecological monitoring and research; Formulate wetland protection planning, strengthen and improve the management system; Adhere to both development and protection, and realize the sustainable development of the lake area. The fragility of Hongze Lake wetland requires us to better protect wetland resources, which is also one of the focuses of future research.